1. Field of the Invention
The present invention relates to a method in which a material is irradiated with an electron beam to produce a higher order Laue zone line of a pattern unique to the material and in which a lattice constant is determined from this higher order Laue zone line, a method of evaluating strain and stress by the use of the method, and an electron microscope suitably used for the method.
2. Description of the Related Art
In general, among main methods of evaluating the state of strain and stress in a material are a strain gauge method, an X-ray diffraction method, a Raman spectroscopy, an FTM method (T. Ide et al., Jpn. J. Appl. Phys. Vol. 37(1998), L1546), and a convergent beam electron diffraction (CBED) method (M. Tanaka and M. Terauchi, Convergent Beam Electron Diffraction, JEOL, Tokyo, 1985). Of these analytical methods, only the CBED method can detect a change in a lattice constant not larger than 10−3 nm in an extremely microscopic region not larger than 10 nm. In particular, the state of stress and strain in an extremely microscopic region of about from 1 to 2 nm can be evaluated by the use of a field emission transmission electron microscope (FE-TEM).
In the development of a semiconductor device and the like, prime importance is placed on the evaluation of stress and strain by the CBED method because of an excellent spatial resolving power. In the CBED method, positions where a plurality of higher order Laue zone lines (HOLZ line) develop are correctly read and the lattice constant of a crystal is calculated from a positional relationship between the HOLZ lines thereby to valuate the stress and strain.
Then, an electron beam is easily entered into a single crystal such as a Si wafer from a specific crystal orientation and the lattice constant can comparatively easily calculated from the positional relationship between the HOLZ lines (for example, Stuer et al., J. Electrochem. Soc. Vol. 148 (2001), G597). However, in a case of evaluation of a polycrystal, the crystal orientations of respective crystal grains are not aligned in one direction, so that it is impossible even to align the incident directions of the electron beam. Against such a background, the evaluation of the polycrystal becomes such a work requiring an enormous amount of time and manpower that records the patterns of HOLZ lines unique to respective crystal grains and uniquely analyzes the patterns one by one to calculate lattice constants thereby to evaluate the stress and strain of each crystal grain.
Thus, in a case where the CBED method is applied to an actual polycrystalline material, a crystal grain having a specific crystal orientation is selected and only the selected crystal grain is evaluated (see Japanese Patent Application Laid-Open No. 7-286915 and the like). At present is required a method of analyzing a HOLZ line of an arbitrary crystal grain of various kinds of crystalline materials with an excellent spatial resolving power of about from 1 to 2 nm and speedily calculating its lattice constant.
That is, there has been conventionally presented a problem of speedily evaluating stress and strain existing in an arbitrary crystal grain existing in an arbitrary polycrystalline material with an excellent spatial resolving power of about from 1 to 2 nm.